Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the zoom lens, which are suitable for an image pickup apparatus using an image pickup element, e.g., a video camera, an electronic still camera, a broadcasting camera, or a monitoring camera, or an image pickup apparatus, e.g., a silver-halide film camera.
Description of the Related Art
In recent years, an image pickup apparatus using an image pickup element is increased in functionality, and the entire apparatus is downsized. Accordingly, as an image pickup optical system to be used in the image pickup apparatus, a compact zoom lens having a short total lens length and a large aperture ratio is demanded.
In Japanese Patent Application Laid-Open Nos. 2006-171431 and 2008-158160, there is described a zoom lens including, in order from an object side to an image side, four lens units having positive, negative, positive, and positive refractive powers, respectively. In the zoom lens described in Japanese Patent Application Laid-Open Nos. 2006-171431 and 2008-158160, the second lens unit and the fourth lens unit are configured to move during zooming.
In this case, in order to achieve a four-unit zoom lens with high optical characteristics while being small as a whole and having a larger aperture ratio, it is important to appropriately set the refractive powers of the respective lens units forming the zoom lens, movement conditions of the respective lens units during zooming, and the like.
For example, it is important to appropriately set the refractive power and the lens configuration of a first lens unit, the refractive power of a second lens unit, and the like. If those configurations are not appropriately set, it is difficult to obtain a zoom lens that is small as a whole, and has a large aperture ratio and high optical characteristics over the entire zoom range.